Safety limit-switch.



wyw. & G. A. PIERCE.

SAFETY LIMIT SWITCH.

APPLIGATION FILED 313.27, 1909.

Patented Sept 27; 1910.

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UNITED STATES PATENT OFTCE.

WILLIAM W. PIERCE AND GEORGE A. PIERCE, 0F PHILADELPHIA, PENNSYLVANIA.

SAFETY LIMIT-SW'ITGH.

To all whom "it may concern.

Be it known that we, WILLIAM WV. Prnuon and Grouse A. Pmucn, citizens ofthe United States, residing in Philadelphia, in the county ofPhiladelphia and State of Pennsylvania, have invented certain new anduseful Improvements in Safety Limit- Switches, of which the following isa specification.

Our invention relates to that class of switches, that are used asprotective devices, and our objects are; first; to provide automaticmeans to prevent a chain block on an electric hoist, or other similardevices, from being moved beyond a predetermined position thereb Yoreventin said chain block from assuming a jamming position to thesupporting structure of said hoist; preventing the breaking of the ropeor gearing attached thereto; protecting the motor or motors connectedtherewith, and to eliminate all possible chance of accidental loss oflife due to any of the above causes; second; to provide automatic meanswhereby after the chain block or other similar device has moved to thepredetermined limiting position, the only possible movement by theoperator is a reverse movement to that w iich brought the device in thelimiting position; third; to provide automatic means whereby a reversemovement of the chain block restores the switch to normal hoisting andlowering position, and fourth; to provide simple means of adjustmentwhereby the safety limit switch can be made to operate at variouslimiting positions.

With these l jects in view, our invention consists in certain novelfeatures of construction and arrangement of parts, as will hereinafterbe more fully described and pointed out in the claims, reference beinghad to the accompanyin drawings form ing part thereof, and in whichFigure 1 is a plan of the safety limit switch in position for normalhoisting and lowering; Fig. 2 an elevation of the safety limit switchand shows more clearly the arrangement of the switch operatingmechanism; Fig. 3 a section on EF, Fig. 1, and shows the method ofinsulating the engaging pin of the switch operating mechanism; Fig. 4 asection on T J, Fig. 1, showing the method of revolubly securing thequick break blades to the saddle embracing the middle blade of theswitch op- Specifioation of Letters Patent.

Application filed February 27, 1909.

Patented Sept. 27, 1910. Serial No. 480,480.

crating mechanism and the method of holding these parts in place; Fig. 5a section on C-D, Fig. 1, through an electric blow-out magnet, showingthe method of securing the magnet core and insulating the same from themagnet winding; Fig. 6 a section on AB, Fig. 1, and shows the method ofinsulating the switch clips from the securing base, also the methodemployed for securing good contact surface between the switch blades andthe switch clips; Fig. 7 a sec tion on GH, Fig. 1, and shows the methodof actuating the adjustable switch mechanism engaging wheel; and Fig. 8a diagram of the electrical connections for said switch, motor,controller and blow-out magnet.

In the accompanying drawings, similar numerals of reference designatecorresponding parts throughout the several views, and in which,

1 designates a base for supporting the switching mechanism.

2 designates a bracket which is rigidly secured upon the base 1 by thescrews 76.

4t designates a screw in threaded engagement with the bracket 2 andlocked in place by a nut 5. Said screws 76 also rigidly secures a plate3 to the base 1. Said plate 3 serves as a bearing for the transmissionwheel 6. In threaded engagement with said wheel 6 is a cap let whichrotatably secures the same to the plate 3.

77 designates a shaft, having secured at one end by threaded engagementthe trans-. mission wheel 6, and which is locked in place by the nut 15.The gear wheel 9 is secured to the other end of said shaft by threadedengagement, and is held in place by the set screw 16. Said gear wheel 9is placed in po sition on the structure of said hoist to be operativewith one of the gears of the operating gear train.

78 designates a shoulder provided on the lower end of the screw 41- andadapted to be inserted in an aperture 79 in the transmission wheel 6.Said transmission wheel revolves on the shoulder 78, motion beingtransmit-ted to said gear wheel 9 from the gear train and this motionretransmitted to the transmission wheel 6 by the shaft 7?.

8 designates an adjustable switch mechanism engaging wheel which isadapted to rotatably traverse the rigid screw e by means of the wristpin 7, which extends from the transmission wheel 6 and is rigidlyattached thereto, and which is inserted in the aperture 10 of the saidwheel.

11 designates a pin rigidly secured to the said wheel 8, and isinsulated therefrom by means of the insulator 12, clearly shown in Fig.3. Said pin 11 is held in rigid relation with said wheel 8 by means ofthe nut 13 in threaded engagement with the shoulder 80 of said pin. Saidwheel 8 is provided with a plurality of apertures, spaced equidistant ona circumference of a circle, whose radius is equal to the distance fromthe center of the wrist pin 7 to the center of the transmission wheel 6.The said gear wheel 9 is placed in mesh with the operating gear train,in such a position that a lowering of the chain block will cause thesaid gear wheel to revolve in such a direction as will move theadjustable switch mechanism engaging wheel 8, away from the switchmechanism. It is obvious that by lowering the chain block a certaindistance, the wrist pin 7 will disengage with the aperture 10 in thesaid wheel 8 and will be free to revolve by hand above the wrist in 7. pThe safety limit switch can be made adjustable to various limitingpositions by selecting a suitable aperture 10 in the said wheel 8,depending on the limiting position, and raising the chain block untilthe wrist pin 7 engages with the selected aperture 10.

18 designates a pedestal bearing, provided with the shoulder 7 (l whichis partly threaded and adapted to engage the nut 19. 2O designates astud rigidly secured to the said bearing 18 by threaded engagement; saidstud and said bearing are insulated from the base 1 by the insulator 81,which is constructed similar to the manner shown in Fig. 3. Said bearing18 is held in rigid relation to'the base 1, by the upper nut 22; thelower nut 22 secures the electrical connection to the stud 20.

17 designates the middle blade of a single pole, double throw, quickbreak, knife switch, revolubly secured to the shoulder 7 O by the nut19. Said middle blade is provided, at one extremity, with the slot 21,which is adapted to engage with the pin 11, carried by the said wheel 8,upon the chain block reaching its predetermined limiting position. It isobvious that a slightly further movement of said wheel 8, will move theswitch blade revolubly to a position as will hereinafter be described,and at the same time disengage the pin 11 and the slot 21. Upon areverse movement of the wheel 8, caused by a reverse movement of thechain block, the pin 11 again engages with the slot 21 and restores theswitch to the position it had heretofore, and upon a further movement ofsaid wheel 8, the said pin disengages with the slot 21.

24 and 25 designates the outer blades of the quick break switch, whichare tapered at the inner lower ends in a manner to reduce their width.35 designates a link connecting the outer blades of said switch and 23designates a saddle embracing said middle blade 17, more clearly shownin Fig. 4.

26 designates a screw, inserted in an aperture in said link 35 and theouter blade 25 and is secured to said saddle by threaded engagement, andlocked in place by the nut 28. 27 designates a similar screw, to that of26 and is inserted in an aperture in the link 35 and the outer blade 24and is secured to said saddle 23 by threaded engagement and locked inplace by the nut 29.

Since the screws 26 and 27 are inserted in apertures in the outer blades25 and 24; it is obvious that said blades can revolve through a certainangular movement, respectively, on said screws 26 and 27.

30 designates an additional link connecting the outer blades 24 and 25and is provided at one end with the slot 34. 32 designates a screwinserted in an aperture in said link 30 and is secured to the outerblade 25 by threaded engagement. 31 designates a similar screw securedto the outer blade 24 by threaded engagement and which is adapted totraverse the slot 34 in the link 30 upon any angular movement of theouter blades 24 and 25.

33 designates a helical spring whose ends are rigidly attached to thescrews 31 and 32. Said helical spring assists a helical spring 41, aswill hereinafter be described, to quickly open the circuit, between theouter blades 24 and 25 and their respective switch engaging clips, whensaid blades have revolved through their maximum angular movement by theswitch actuating mechanism. Said spring also serves to keep thedisengaged switch blade in position against the middle blade 17, thuspreventing said blade from making an undesirable electrical connectionwith its respective switch clip.

45 designates a block, insulated from the base 1 by the insulator 54 andhas the stud 51 secured thereto by threaded engagement. Said block isrigidly secured to the base 1 by the upper nut 52, while the lower nutserves to secure the electrical connection to said stud.

71 designates a rod, rigidly secured at one end to the block 45 bythreaded engagement. Embracing said rod are the switch clips 46 and 47separated by the distance piece 48; said clips and said distance pieceare prevented from turning on the rod 71 by the pin 49, which is rigidlysecured to the block 45. 53 designates a helical spring embracing thesaid rod 71 and held on the same by the nut 50. It is obvious thatvarious tensions can be exerted by the spring 53, by adjusting said nutwith respect to said rod. The lower part of the spring being in contactengagement with said clips, it is obvious that when the same are inengagement with their respective switch blades, that sutticient pressurecan be exerted by said spring on said clips to insure goodcontactsurface between said blade and said clips.

designates a cylindrical base, which is rigidly attached to the base 1by means of the nut (54 in threaded engagement with the lower threadedportion (33. The said base 65 is insulated from the base 1, by the insulator 82 in a manner similar to the method shown in Fig. 3.

eat designates a rod, provided with a slot 38 at one end, adapted toengage with the spindle 39; the other end being reduced to a fiat whichis revolubly secured to the middle blade 17 by the screw 37, in threadedengagement therewith, and locked in place by the nut i2. 90 designates apin in rigid relation with the flattened end of said rod M, andintermediate of said pin and said spindle is the helical spring 41,provided at each end with the washers l0 and 72. Said pin 90 confinesthe movement of the washer 72 toward said flat end of the rod d4. It isobvious that upon the movement of the middle switch blade 17 toward amid position bet-ween said contact clips, that the helical spring 41will be placed under compression, which will be at its maximum at themid position. It is also obvious that upon the revolving of the middleswitch blade 17, the engaged outer blade will remain in contact with itsswitch clip, due to the pressure exerted by the helical spring 53 actingthereon. Said outer blade will, however revolve on the screw 31 untilthe tapered edge of the same engages with the edge of the middle blade17, and which will occur when the middle blade 17 has moved slightlypast the mid position and after the pin 11 has disengaged with the slot21. It is also obvious that at this position, the spring 33 will beunder tension, and upon further movement of the middle blade 17 past themid position, the pin 11 disengages with the slot 21. It is furtherobvious that upon the disengaging ot the pin 11 with the slot 21, thatthe helical spring all will be free to quickly expand, which will movethe middle blade 17, into engagement with the tapered edge of theengaged outer blade and withdraw the engaged outer blade out ofengagement with its switch clip. The cooperation of the springs 41 and33 will quickly break the circuit that heretofore ex isted and throwinto engagement the heretofore disengaged outer blade with itsrespective switch clip.

58 designates the winding of a magnetic blow out magnet, 56 the core and(31 the pole pieces. Said winding 58 is insulated from the core 56 andthe pole pieces 61 by the insulator 57. 55 designates non-magneticsupports for said magnet, having the core 56 secured thereto by threadedengagement and locked in place by the nut (50. Said supports are rigidlysecured to the base 1 by the screws 62.

9S designates the operating motor arma ture, 85 the field windingtherefor and 99 designates the controller.

a, S6, 87, 88, so, 91, 92, as, at and a5 designates connecting leads forthe aforesaid parts.

L H designates the normal switch engag ing clip, and upon this positionnormal hoisting and lowering can take place, dependent upon the positionof the controller.

L designates the safety position clip and upon this position, a loweringmovement only can take place.

The foregoing apparatus is suitably pro portioned and mounted upon anappropriate base and operatively connected to a gear in the operatingtrain of gears, all of which will be readily understood by those skilledin the art to which this invention relates. Its mode of operation willbe substznitially as follows: in mesh with or actuated by one of thegears of the operating gear train, is placed the gear wheel 9. The saidgear wheel, being in rigid relation to the transmission wheel (3,revolves the same upon the operation of the gear train. The wrist pin 7being in rigid relation to the transmission wheel (3 and in engagementwith a predetermined aperture 10 in the switch mechanism engaging wheel8, .revolubly traverses the said wheel 8 upon the screw upon theoperation of the gear train. The gear wheel 9 and the screw are soproportioned, that the extreme travel of the hoist will bring the pin11, which revolves with the said wheel 8, in engagement with the slot 21of the middle blade 17. The switch is shown in position, Fig. 1, fornormal hoisting and lowering, and the pin 11 about to en age with slot21 upon the limiting position having nearly been reached.

By referring to Fig. 8 the controller 99 is shown in the ofif position.It will be seen that normal hoisting and lowering can be efiected asfollows:

Normal hoistingr-Positive side of line to controller 99, leads 91, 92,outer blade 2%, lead 93, motor armature 98, leads 9%, 95, to controller99, from controller 99, leads 89, 86, motor field 85, lead 8% and backto negative side of line.

Normal Z0wer2'ng.Positive side of line to controller 99, leads 95, 91,motor armature 98, lead 93, outer blade 24., leads 92, 91, to controller99, from controller 99 by lead 89, lead 86, motor field 85, lead 8% andback to negative side of line.

Upon the engagement of the pin 11 with the slot 21 of the middle blade17 upon abnormal hoisting, mot-ion will be transmitted to the said bladeupon further movement of the pin 11. The movement of the said bladecauses the outer blade 24: to revolve, until the tapered inner edge isin engagement with the edge of the middle blade 17, the outer blademeanwhile remaining in contact with its engaging switch clip. lVhen themiddle blade 17 has moved slightly beyond the mid position of the switchclips, the pin 11 will have passed out of engagement with the slot 21.The helical spring 41 will then quickly move the middle blade 17 untilthe inner tapered edge of the outer blade 24 is in engagement with theedge of the middle blade 17 The concerted action of the helical springs41 and 33 will then quickly move the middle blade 17 and the outer blade24 to pull out of engagement the outer blade 24; and its engaging switchclip. The magnetic blow out winding, being always in circuit with theline, will magnetize the core 56 and the pole pieces 61 and on accountof the well known property of magnetism to deflect the arc of anelectric circuit, will assist upon the breaking of the circuit betweenthe outer blade 24 and its engaging clip, to quickly break the arcconsequent to the breaking of the circuit, and thereby prevent burningof the outer blades 24: and 25 and their engaging clips.

Referring to the wiring diagram of connections Fig. 8, it will beevident that the operator cannot elevate the hoist, and the onlypossible movement, is a reverse one to that which brought the hoist inthe limiting position, namely lowering, as follows, positive line,controller 99, leads 95 and 94, motor armature 98, lead 93, outer blade25, leads 8-7 and 86, motor field 85, lead 8 1 and back to negative sideof line.

The foregoing description is applicable where the limit switch is usedto prevent abnormal hoisting. It is also obvious that the limit switchcan also be used to prevent abnormal lowering.

The foregoing movements accomplish the hereinbefore mentioned first andsecond objects of our said invention.

Upon the engagement of the outer blade 25 and its engaging clip, thelowering of the hoist will impart a reverse motion to the pin 11, whichwill again engage with the slot 21 and move the middle blade 17 in areverse direction, past the mid position of the engaging clips. The pin11 will then disengage with the slot 21 and the helical springs 41 and33 will then coact to quickly break the circuit between the outer blade25 and its engaging clip and throw into en gagement the outer blade 24and its engaging clip; the magnetic blow out, assisting to break the areupon the breaking of the electric circuit. The foregoing movementsaccomplish the hereinbefore mentioned third object of our saidinvention.

By lowering the hoist, until the wrist pin 7, disengages with theaperture 10, the adjustable switch mechanism engaging wheel 6 can berotated by hand on the screw 4:, above the wrist pin 7. By selecting asuitable aperture 10 in the said wheel 6, dependent on the limitinghoisting position and by elevating the hoist and turning the said wheel,the wrist pin 7 can be made to engage with the desired aperture and theswitch made to operate at Various limiting positions and therebyaccomplish the hereinbefore mentioned fourth object of our saidinvention.

It is obvious that departures can be made from the general features ofconstruction of our said invention, especially, means for actuating theswitching mechanism, imparting motion thereto and without departing fromthe spirit and intent thereof; therefore .Vhat we claim as new anddesire to secure by Letters Patent is 1. In a limit switch of thecharacter described, the combination with a switching mechanism, of afixed screw, a member adapted to rotatably traverse the said screw, saidmember adapted to engage with and actuate said switching mechanism upona predetermined movement of said member, a transmission means, a crankoperatively connected to the transmission means and adapted to engagewith said member, all substantially as and for the purpose shown anddescribed.

2. In a limit switch of the character described, the combination with asingle pole, double throw, switch, the blade of which is pivoted at oneof its extremities and provided with a slot, of a fixed screw, a wheeladapted to rotatably traverse said screw, a pin rigidly attached to saidwheel and adapt ed to engage with the slot of said switch blade,coacting resilient members to actuate said switch upon a predeterminedmovement of said wheel and to react on the same upon the reversesubsequent movement thereof, a transmission means, a crank operativelyconnected to the transmission means, a plurality of apertures in saidwheel and adapted to engage with the crank wrist of said crank, allsubstantially as and for the purpose shown and described.

3. In a limitswitch of the character clescribed, the combination with asingle pole double throw switch provided with a main switch blade andadjacent switch blades, switch clips adapted to engage therewith, a yokeprovided on the main blade of said switch at its pivotal end, of a fixedscrew, a wheel provided with a plurality of apertures adapted torotatably traverse the said screw, a pin rigidly attached to said wheeland adapted to engage with said yoke, a helical compression springattached to one end of said main blade and pivoted at a pointequidistant in relation to said switch clips, a helical springconnecting the said adjacent switch blades together, said springsadapted to actuate said adjacent switch blades upon a predeterminedmovement of said wheel and to reactuate the same upon the reversesubsequent movement thereof, a transmission means, a crank operativelyconnected to said transmission means, and a crank wrist on said crankadapted to engage with the said apertures in the said wheel, allsubstantially as and for the purpose shown and described.

4. In a limit switch of the character described, the combination with asingle pole double throw switch provided with a main switch blade andadjacent switch blades; switch clips adapted to engage therewith; a yokeprovided on the main blade of said switch at its pivotal end; of a fixedscrew, a wheel provided with a plurality of apertures adapted torotatably traverse the said screw, a pin rigidly attached to the saidwheel and adapted to engage with said yoke,

a helical compression spring attached to one end of said main blade andpivoted at a point equidistant in relation with the said switch clips, ahelical spring connecting the said adjacent switch blades together, saidsprings adapted to actuate the said adjacent switch blades upon apredetermined movement of said wheel and to reactuate the same upon thereverse subsequent movement thereof, a transmission means, and a meansactuated thereby to engage with the apertures in said wheel to actuatethe said switch, all substantially as and for the purpose shown anddescribed.

In testimony whereof, we have hereunto signed our respective names tothis specification in the presence of two subscribing witnesses.

KVILLIAM \V. PIERCE. GEORGE A. PIERCE.

\Vitnesses J. Oscar: GEUTHER, ALBERT H. THOMAS.

